Transcription And Translation

Question 1

What is translation?

Answer 1

A proccess to translate a rna code into protein

Question 2

What are the different types of RNA?

Answer 2

rRNA, mRNA, tRNA, miRNA, non coding RNA

Question 3

What are the three stages of transcription?

Answer 3

Initiation, elongation, and termination.

Question 4

How is the process started?

Answer 4

A promoter protein binds to a promoter sequence on DNA, and general transcription factors help to unwind the DNA chains so that RNA polymerase can work.

Question 5

How is the process regulated?

Answer 5

Additional consensus sequences upstream of the promoter, proximal regulatory elements (near promotion sites, affect frequency of transcription initiation) and distal regulatory elements, (further away from promotion sites and monitor the response to hormones)

Question 6

How is RNA processed?

Answer 6

5’ capping, poladenlyation (3’ end) and splicing (removal of introns)

Question 7

How does splicing work?

Answer 7

Introns are removed from the protein, whereas exons remain. It is a process mediated by small nuclear RNA’s.

Question 8

What is transcription?

Answer 8

The proccess of changing a dna code into a rna code

Question 9

Where does translation occur?

Answer 9

On ribosomes, often on the rough endoplasmic reticulum.

Question 10

What are the key features of eukaryotic ribosomes?

Answer 10

40S + 60S subunits, 80S ribosome, contains 4 rRnA’s and 82 proteins

Question 11

What are the key features of the structure of tRNA?

Answer 11

A stem loop, -oH on phosphate end used to bind with an aminoacid and an anticodon on the other end that binds to an amino acids.

Question 12

What are the three binding sites for tRNA on a ribosome?

Answer 12

A, P and E sites

Question 13

What happens at the A, P and E sites of a ribosome?

Answer 13

A site binds the incoming aminoacyl tRNA as directed by the codon occupying the site, P site is occupied by a tRNA with the already synthesised amino acid chain, and the P site is occupied by a TRNA about to exit the ribosome.

Question 14

What are the key features of the genetic code?

Answer 14

Specificity, universality, degeneracy.

Question 15

What is the translation start codon?

Answer 15

AUG

Question 16

What are the termination codons for translation?

Answer 16

UGA, UAG, UAA

Question 17

What is the wobble hypothesis?

Answer 17

The last amino acid of a codon is the wobble position, and allows a certain degree of flexibility in the last base of the codon, meaning that one tRNA can work with more than one codon.

Question 18

What are the key features of initiation of protein translation?

Answer 18

The small ribosomal subunit binds to the 5’cap of the mRNA, until in encounters the start codon AUG, which is recognised by a initiator tRNA that binds to the the P site allowing the stages of termination to start.

Question 19

What are the key features of elongation in translation?

Answer 19

Ribosome moves 5’to 3’ , tRNA is delivered to A site, formation of peptide bond catalyses by peptidyl transferase , translocation is used to advance the mRNA to the 3 prime end (requiring GTP hydrolysis) uncharged tRNA moved to the p site for release .

Question 20

Describe the termination of translation.

Answer 20

Occurs when one of 3 termination codons moves into A site, release factors cause hydrolysis of bond linking peptide to tRNA at p site. The protein may undergo further modification.

Question 21

What is a polysome?

Answer 21

Because of the length of mRNA, more than one ribosome may be required which creates a polysome, with more than one ribosome on a mRNA.

Question 22

Give a brief description of the process of transcription.

Answer 22

RNA binds to a transcription factor complex in the promoter region (in eukaryotes this is a TATA box), unwinds at point near start point of transcription, strands unwind as RNA polymerase approaches and rejoin as the polymerase approaches, transcription factor is released once the RNA as it is about 10 bases long, and continues until a rna sequence is reached.

Question 23

What does the enzyme peptidyl transferase do?

Answer 23

Catalyses the formation of a peptide bond between the two amino acid, and assist in the translocating of an amino acid from the a site to the p site